Set vs Update for complex list elements

We have the following behavior currently in 8.10 and 7.10:

If we have a doc with a complex property of {"foo": "foo1", "bar": "bar1"} and set the complex property (using setPropertyValue) to {"bar": "bar2"} then re-reading the property gives {"foo": "foo1", "bar": "bar2"}.
Let's denote this by:

{"foo": "foo1", "bar": "bar1"} & {"bar": "bar2"} -> {"foo": "foo1", "bar": "bar2"}

This means that setProperty actually does an update and not a replace, which IMHO unexpected.
If we have a list of complex properties, the behavior is basically the same.

So in 7.10/8.10 we have:

 {"foo": "foo1", "bar": "bar1"}  &  {"bar": "bar2"}  ->  {"foo": "foo1", "bar": "bar2"}
[{"foo": "foo1", "bar": "bar1"}] & [{"bar": "bar2"}] -> [{"foo": "foo1", "bar": "bar2"}]

However previously in 6.0 and before we had a different and internally inconsistent behavior:

 {"foo": "foo1", "bar": "bar1"}  &  {"bar": "bar2"}  ->  {"foo": "foo1", "bar": "bar2"}
[{"foo": "foo1", "bar": "bar1"}] & [{"bar": "bar2"}] -> [{"bar": "bar2"}]

So the list case behaved like a replace while the direct complex property case behaved like an update.

None of this is satisfactory. Ideally this is the behavior we want because it provides the least surprise:

 {"foo": "foo1", "bar": "bar1"}  &  {"bar": "bar2"}  ->  {"bar": "bar2"}
[{"foo": "foo1", "bar": "bar1"}] & [{"bar": "bar2"}] -> [{"bar": "bar2"}]

The question is how to deal with backward compatibility...

Note that someone that really wants to update just a sub-property and not replace the other fields can always just do that using doc.getProperty("complex/foo").setValue("foo2").